Halogenated ester derivatives

ABSTRACT

New halogenated ester derivatives and liquid crystal compositions containing the same are provided. The derivatives are expressed by the general formula ##STR1## wherein X is ##STR2## R is 1-15C alkyl group or alkoxy group; and Y is carboxyl group. The derivatives are useful as component(s) of liquid crystal compositions which have higher mesomorphic temperature ranges, nevertheless have lower viscosities; and also have lower absolute values of dielectric anisotropy, nevertheless can be driven at lower voltages.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to new halogen-containing compounds, preferablyfluorine-containing compounds, having a positive dielectric anisotropy,useful as components of liquid crystal compositions, and also it relatesto liquid crystal compositions containing the same.

2. Description of the Prior Art

Display elements in which liquid crystals are incorporated have beenwidely used for clocks, electronic calculators, etc. These liquidcrystal display elements utilize the optical anisotropy and dielectricanisotropy of liquid crystal substances, and liquid crystals includenematic ones, smectic ones and cholesteric ones. Among them, displayelements utilizing nematic liquid crystals have been most widelyemployed practically, and include TN (twisted nematic) type, DS (dynamicscattering) type, guest-hot type, DAP type, etc. Specific featuresrequired for the liquid crystal substances vary depending on therespective types of display elements. Anyhow, however, the liquidcrystal substances employed in these display elements are preferred toexhibit a liquid crystal phase within as broad a range as possible inthe natural environment. But no single substance is now present whichsatisfies by itself the above-mentioned conditions, but it is thepresent status of the art that several kinds of liquid crystalsubstances or non-liquid crystal substances are mixed together to obtainsubstances which are fit for practical purpose for the present. Further,these substances must, of course, be stable against moisture, light,heat, air, etc. and also it is preferred that their threshold voltagesand saturation voltages required for driving the display elements be aslow as possible and their viscosities be also as low as possible forreducing the response time. Now, in order to extend the mesomorphictemperature ranges toward higher temperatures, it is necessary to employliquid crystal substances having higher melting points as a component orcomponents of liquid crystal composition, but such liquid crystalsubstances having higher melting points generally have higherviscosities; hence liquid crystal compositions containing thecomponent(s) also have higher viscosities. Accordingly, liquid crystaldisplay elements which are employable up to higher temperatures e.g. upto about 80° C. have had a tendency that their response times areretarded and notably retarded particularly at lower temperatures. Thus,liquid crystal substances having higher mesomorphic temperature rangesand nevertheless having lower viscosities have been desired. On theother hand, those having larger absolute values of dielectric anisotropyhave generally been required. Because, by employing liquid crystalcompositions having larger absolute values of dielectric anisotropy, itis generally possible to lower the drive voltage for display elementsand also improve the response characteristics. Further, if liquidcrystals which have no larger absolute values of dielectric anisotropy,nevertheless can effect drive at lower voltages are found, then it willbe possible to further reduce power consumption for display elements;hence such liquid crystals are more desirable.

The present inventors have made broad researches for obtaining compoundssatisfying these desires, and have found that certain kinds ofhalogen-containing compounds, particularly fluorine-containingcompounds, satisfy such requirements.

SUMMARY OF THE INVENTION

One aspect of the present invention resides in: halogenated esterderivatives expressed by the general formula ##STR3## wherein Xrepresents a group selected from the group consisting of ##STR4## Rrepresents an alkyl group or an alkoxy group, each having 1 to 15 carbonatoms; and Y represents carboxyl group.

Another aspect of the present invention resides in:

liquid crystal compositions comprising as at least one componentthereof, a halogenated ester derivative or derivatives expressed by theabove general formula (I).

The compounds of the general formula (I) have small values of dielectricanisotropy in the vicinity of Δε=1.5, nevertheless they or liquidcrystal compositions containing them as a component or componentsthereof have as low a threshold voltage as about 1.4 to 2.0 V to makedrive at lower voltages possible. Thus, it is possible to producedisplay elements of small consumption of power by employing thesecompounds. Further, they have a sufficient stability against heat,light, humidity, electricity, etc. required as liquid crystals fordisplay elements.

Next, the method for preparing the compounds of the present inventionwill be mentioned.

First in the case of halogenophenyl esters of carboxylic acids expressedby the general formula ##STR5## wherein X and Hal are the same as thosedefined above in the general formula (I), they can be obtained byreacting thionyl chloride with a carboxylic acid corresponding to thesubstituent X to prepare a carboxylic acid oxychloride which is thenreacted with a 4-halogenophenol in the presence of pyridine.

Further, in the case of compounds expressed by the general formula##STR6## wherein X represents ##STR7## and R is the same as definedabove in the formula (I), they can be obtained by first reacting thionylchloride with 4-fluorobenzoic acid to prepare 4-fluorobenzoic acidoxychloride which is then reacted with a 4-substituted phenol or atrans-4-substituted cyclohexanol or the like corresponding to the aimedproduct, in the presence of pyridine.

As for compounds as obtained above, some of them are of nematic liquidcrystals and others are of smectic ones and further there are compoundswhich do not constitute any liquid crystal by themselves. Anyhow,however, since they have a small dielectric anisotropy, it is possibleto obtain liquid crystal display elements having a smaller dielectricanisotropy and also a lower drive voltage, when the above-mentionedcompounds are combined with other liquid crystal compounds to prepareliquid crystal compositions. Such other liquid crystal compounds may beappropriately selected depending on types of display elements, uses,etc. Since the above-mentioned compounds are well compatible with otherliquid crystal compounds, there is almost no restriction in thisrespect.

The compounds of the present invention will be further illustrated indetail by way of Examples showing the preparation examples of thecompounds of the present invention expressed by the formula (I), thecharacteristic values of the compounds thus prepared and thecharacteristic values of liquid crystal compositions containing theabove compounds.

EXAMPLE 1

[Preparation of 4'-fluorophenylesters of trans-4-substitutedcyclohexanecarboxylic acids expressed by the formula ##STR8## (IV)]

Thionyl chloride (10 ml) is added to trans-4-substitutedcyclohexanecarboxylic acid (0.03 mol), and the mixture is heated on awater bath at 60° to 80° C. for 4 hours, after which the mixture becomesuniform and then allowed to stand further for one hour, followed bycompletely distilling off excess thionyl chloride under reduced pressureto leave an oily substance, which is trans-4-substitutedcyclohexanecarboxylic acid oxychloride.

This oxychloride is then added with vigorous stirring to a solution of4-fluorophenol (3.3 g) dissolved in pyridine (10 ml). The resultingreaction liquid is allowed to stand overnight and then added to water(100 ml), followed by extracting the resulting oily substance withtoluene (100 ml). The resulting toluene layer is washed with 6 N HCl andthen with 2 N NaOH and then washed with water till the layer becomesneutral. After filtration of the toluene layer, toluene is distilled offunder reduced pressure. A remaining oily substance is recrystallizedfrom ethanol to give the objective 4'-fluorophenyl ester oftrans-4-substituted cyclohexanecarboxylic acid. The physical properties(transition points) and values of elemental analysis of a series ofcompounds obtained as above are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                              Value of                                                                      elemental analysis                                      Transition point                  The-                                        R in                   M.P. or N--I     Ob-   oret-                           formula                                                                              Yield   Yield   C--N point                                                                            point    served                                                                              ical                            (IV)   (g)     (g)     (°C.)                                                                          (°C.)                                                                           (%)   (%)                             ______________________________________                                        C.sub.3 H.sub.7                                                                      6.1     77.0      48˜48.7                                                                       --   C   72.5  72.7                                                                H   7.8   8.0                             C.sub.4 H.sub.9                                                                      3.1     37.2    30.8˜31.1                                                                       --   C   73.6  73.4                                                                H   8.4   8.3                             C.sub.5 H.sub.11                                                                     3.6     41.1    25.9˜26.0                                                                       23.1 C   74.1  73.9                                                                H   8.8   8.6                             C.sub.6 H.sub.13                                                                     4.5     49.0    29.7˜30.0                                                                       24.3 C   74.3  74.5                                                                H   8.7   8.9                             C.sub.7 H.sub.15                                                                     5.9     61.5    29.1˜29.3                                                                       33.2 C   75.2  75.0                                                                H   9.3   9.1                             C.sub.8 H.sub.17                                                                     6.0     59.9    34.1˜34.7                                                                       30.6 C   75.6  75.4                                                                H   9.1   9.3                             C.sub.6 H.sub.13 O                                                                   5.5     56.9    35.6˜35.9                                                                       --   C   70.5  70.8                                                                H   8.8   8.4                             ______________________________________                                    

EXAMPLE 2

[Preparation of 4'-fluorophenyl esters of 4-substituted benzoic acidsexpressed by ##STR9## (V)]

Example 1 was repeated except that 4-substituted benzoic acids (0.03mol) were substituted for trans-4-substituted cyclohexanecarboxylicacids in Example 1, to obtain 4'-fluorophenyl esters of 4-substitutedbenzoic acids. The physical properties and values of elemental analysisof these compounds are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                                Value of                                                           Transition point                                                                         elemental analysis                                                           M.P. or                The-                            R in                   C--Sm  Sm→I                                                                             Ob-   oret-                           formula                                                                              Yield   Yield   point  point     served                                                                              ical                            (V)    (g)     (%)     (°C.)                                                                         (°C.)                                                                            (%)   (%)                             ______________________________________                                        C.sub.3 H.sub.7                                                                      4.5     58.1    48.1˜                                                                          --    C   74.8  74.4                                                   49.4         H   6.1   5.9                             C.sub.4 H.sub.9                                                                      4.7     57.6    37.2˜                                                                          --    C   74.8  75.0                                                   38.0         H   6.5   6.3                             C.sub.5 H.sub.11                                                                     4.2     48.9    32.9˜                                                                          --    C   75.8  75.5                                                   33.8         H   6.5   6.7                             C.sub.7 H.sub.15                                                                     4.9     52.0    35.1˜                                                                          --    C   76.8  76.4                                                   35.5         H   7.2   7.4                             C.sub.8 H.sub.17                                                                     5.1     51.8    41.7˜                                                                          --    C   76.9  76.8                                                   42.8         H   7.1   7.7                             CH.sub.3 O                                                                           5.7     77.2    56.1˜                                                                          --    C   68.9  68.3                                                   57.4         H   4.7   4.5                                                    (60.8˜                                                                  61.6)*                                                 C.sub.2 H.sub.5 O                                                                    5.5     70.5    70.5˜                                                                          --    C   69.8  69.2                                                   71.3         H   5.1   5.0                                                    (77.4)*      H   5.1   5.0                             C.sub.3 H.sub.7 O                                                                    5.9     71.8    81.1˜                                                                          --    C   69.9  70.1                                                   82.2         H   5.3   5.5                             C.sub.4 H.sub.9 O                                                                    6.0     69.4    97.5˜                                                                          --    C   70.6  70.8                                                   98.5         H   6.2   5.9                             C.sub.5 H.sub.11 O                                                                   6.0     66.2    66.5˜                                                                          --    C   71.1  71.5                                                   68.1         H   6.5   6.3                             C.sub.6 H.sub.13 O                                                                   6.2     68.4    59.0˜                                                                          37.1  C   72.3  72.1                                                   60.4         H   6.9   6.7                             C.sub.7 H.sub.15 O                                                                   7.0     70.7    64.6˜                                                                          40.6  C   72.5  72.7                                                   66.1         H   6.9   7.0                             C.sub.8 H.sub.17 O                                                                   6.9     66.9    58.2˜                                                                          42.5  C   73.0  73.2                                                   58.8         H   7.5   7.3                             ______________________________________                                         *Value of a different crystalline form                                   

EXAMPLE 3

[Preparation of 4"-fluorophenyl ester of4-(trans-4'-pentylcyclohexyl)-benzoic acid expressed by the formula##STR10##

Example 1 was repeated except that 4-(trans-4'-pentylcyclohexyl)-benzoicacid (0.03 mol) was substituted for trans-4-substitutedcyclohexanecarboxylic acids in Example 1, to obtain 4"-fluorophenylester of 4-(trans-4'-pentylcyclohexyl)-benzoic acid (7.5 g) (yield:67.9%), which also was of a smectic liquid crystal and had a C-Sm pointof 91.0°˜93.3° C. and a Sm-I point of 159.0° C. Further, the values ofelemental analysis were C: 79.9% (theoretical: 78.2%) and H: 7.8%(theoretical: 7.9%).

EXAMPLE 4

[Preparation of 4'-fluorophenyl esters of 6-substitutednaphthalene-2-carboxylic acids expressed by the formula ##STR11## (X)]

Example 1 was repeated except that 6-substitutednaphthalene-2-carboxylic acids (0.03 mol) were substituted fortrans-4-substituted cyclohexanecarboxylic acids in Example 1, to obtain4'-fluorophenyl esters of 6-substituted naphthalene-2-carboxylic acids.Their values of physical properties are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        R in              Transition point                                            formula  Yield   Yield    M.P.    Sm--I point                                 (X)      (g)     (%)      (°C.)                                                                          (°C.)                                ______________________________________                                        C.sub.5 H.sub.11                                                                       5.1     50.6     83.3˜89.2                                                                       --                                          C.sub.7 H.sub.15                                                                       5.0     45.8     67.0˜69.0                                                                       --                                          C.sub.5 H.sub.11 O                                                                     6.2     72.9      97.7˜100.0                                                                     --                                          C.sub.8 H.sub.17 O                                                                     6.5     55.0     74.0˜76.3                                                                       70.0                                        ______________________________________                                    

EXAMPLE 5

[Preparation of 4'-fluorophenyl esters of6-substituted-1,2,3,4-tetrahydronaphthalene-2-carboxylic acids expressedby the formula ##STR12##

Example 1 was repeated except that6'-substituted-1,2,3,4-tetrahydronaphthalene-2-carboxylic acids (0.03mol) were substituted for trans-4-substituted cyclohexanecarboxylicacids in Example 1, to obtain 4'-fluorophenyl esters of6-substituted-1,2,3,4-tetrahydronaphthalene-2-carboxylic acids. In thecase of R=C₅ H₁₁ in the above formula, the resulting product wasobtained with a yield of 5.5 g (53.9%) and had a m.p. of 77.0°˜78.6° C.,and in the case of R=C₇ H₁₅, the yield was 6.1 g (55.3%) and the m.p.was 58.6°˜59.7° C.

EXAMPLE 6

[Preparation of 4"-halogenophenyl esters oftrans-4-(trans-4'-substituted cyclohexyl)-cyclohexanecarboxylic acidsexpressed by the formula ##STR13##

Thionyl chloride (10 ml) was added to trans-4-(trans-4'-substitutedcyclohexyl)-cyclohexanecarboxylic acid (0.02 mol), followed by heatingat a temperature of 60° to 80° C. It takes about one hour till themixture becomes uniform. It is further heated for about 30 minutes toone hour, followed by distilling off excess thionyl chloride underreduced pressure. The resulting remaining oily substance corresponds totrans-4-(trans-4'-substituted cyclohexyl)-cyclohexanecarboxylic acidoxychlorides, which are then added to a solution of a 4-halogenophenol(0.2 mol) in pyridine (10 ml). The resulting reaction mixture issufficiently agitated and allowed to stand overnight, followed by addingtoluene (100 ml), washing the resulting toluene layer first with 6 Nhydrochloric acid, then with 2 N sodium hydroxide solution and finallywith water till it becomes neutral, with a separating funnel, dryingover anhydrous sodium sulfate and distilling off toluene under reducedpressure. The resulting precipitated crystals are recrystallized fromethanol (200 ml) to obtain compounds expressed by the formula (XI) asthe objective products. Their yields, physical properties (transitionpoints) and values of elemental analysis are shown in Table 4.

                                      TABLE 4                                     __________________________________________________________________________           Amount of                       Value of                                      raw material                                                                         Amount of       Transition point                                                                       elemental analysis                     In formula                                                                           carboxylic                                                                           halogenophenol        N--I      Theo-                           (XI)   acid used                                                                            used    Yield                                                                             Yield                                                                             C--N point                                                                          point                                                                              Observed                                                                           retical                         R   Hal                                                                              (g)    (g)     (g) (%) (°C.)                                                                        (°C.)                                                                       (%)  (%)                             __________________________________________________________________________    C.sub.3 H.sub.7                                                                   F  5      2.2     4.0 58  69.4˜70.5                                                                     183.1                                                                            C 76.1 76.3                                                                   H 8.8  9.0                             C.sub.7 H.sub.15                                                                  F  6.1    2.2     4.0 5.0 73.7˜74.3                                                                     170.1                                                                            C 77.2 77.6                                                                   H 9.9  9.8                             C.sub.3 H.sub.7                                                                   Cl 5      2.6     4.5 62  82.4˜82.8                                                                     214.9                                                                            C 72.9 72.8                                                                   H 8.5  8.6                                                                    Cl                                                                              9.7  9.8                             C.sub.7 H.sub.15                                                                  Cl 6.1    2.6     4.7 54  86.0˜87.2                                                                     196.8                                                                            C 74.4 74.5                                                                   H 9.6  9.4                                                                    Cl                                                                              8.5  8.5                             __________________________________________________________________________

EXAMPLE 7

[Preparation of 4'-substituted phenyl esters of 4-fluorobenzoic acids(VIII)]

Thionyl chloride (7 ml) is added to 4-fluorobenzoic acid (2.8 g) (0.02mol), and the mixture is heated on a water bath at 60° to 80° C. for 4hours, after which the mixture becomes uniform and is then allowed tostand further for one hour, followed by completely distilling off excessthionyl chloride. The resulting remaining oily substance corresponds to4-fluorobenzoic acid oxychloride, which is added with vigorous stirringto a solution of a 4-substituted phenol (0.02 mol) in pyridine (7 ml).The resulting reaction liquid is allowed to stand overnight, and thenadded to 100 ml of water, followed by extracting the resulting oilysubstance with 100 ml of toluene. The resulting toluene layer is washedwith 6 N HCl, then with 2 N NaOH and further with water till it becomesneutral, followed by filtration and distilling off toluene under reducedpressure. The resulting remaining oily substance is recrystallized fromethanol to obtain a 4'-substituted phenyl ester of 4-fluorobenzoic acid.Their values of phisical properties and values of elemental analysis areshown in Table 5.

                  TABLE 5                                                         ______________________________________                                                           Value of                                                                      elemental analysis                                         R in                                       Theo-                              formula                                                                              Yield   Yield   M.P.        Observed                                                                              retical                            (VIII) (g)     (%)     (°C.)                                                                              (%)     (%)                                ______________________________________                                        CH.sub.3 O                                                                           3.6     73.2    86.6˜87.0                                                                       C   68.1    68.3                                                              H   4.2     4.5                                C.sub.2 H.sub.5 O                                                                    3.9     75.0    84.8˜85.3                                                                       C   70.0    69.2                                                              H   4.8     5.0                                C.sub.3 H.sub.7 O                                                                    3.6     65.7    73.3˜74.0                                                                       C   69.9    70.1                                                              H   5.6     5.5                                C.sub.4 H.sub.9 O                                                                    4.2     72.9    73.0˜73.2                                                                       C   70.5    70.8                                                              H   6.0     5.9                                C.sub.5 H.sub.11 O                                                                   4.1     67.9    67.0˜67.5                                                                       C   71.1    71.5                                                              H   6.4     6.3                                C.sub.6 H.sub.13 O                                                                   4.9     77.5    64.8˜65.1                                                                       C   72.3    72.1                                                              H   6.6     6.7                                C.sub.7 H.sub.15 O                                                                   5.3     80.3    74.8˜75.7                                                                       C   72.5    72.7                                                              H   7.1     7.0                                CH.sub.3                                                                             2.9     54.3    74.8˜75.4                                        C.sub.2 H.sub.5                                                                      3.1     63.5    51.1˜52.1                                        C.sub.3 H.sub.7                                                                      3.5     67.8    30.0˜31.0                                        C.sub.4 H.sub.9                                                                      3.7     55.1    46.7˜47.7                                        C.sub.5 H.sub.11                                                                     4.0     69.9    35.2˜36.2                                        C.sub.6 H.sub.13                                                                     4.3     71.7    42.3˜42.8                                        C.sub.7 H.sub.15                                                                     4.5     71.7    42.3˜43.3                                        ______________________________________                                    

EXAMPLE 8

[Preparation of trans-4'-substituted cyclohexyl esters of4-fluorobenzoic acid (IX)]

Example 7 was repeated except that trans-4-substituted cyclohexanols(0.02 mol) were substituted for 4-substituted phenols in Example 7, toobtain trans-4'-substituted cyclohexyl esters of 4-fluorobenzoic acid.Their values of physical properties and values of elemental analysis areshown in Table 6.

                  TABLE 6                                                         ______________________________________                                                           Value of                                                                      elemental analysis                                         R in                                      Theo-                               formula                                                                              Yield   Yield   M.P.        Observed                                                                             retical                             (IX)   (g)     (%)     (°C.)                                                                              (%)    (%)                                 ______________________________________                                        C.sub.3 H.sub.7                                                                      3.1     58.9    45.0˜45.5                                                                       C   72.9   72.7                                                               H   7.9    8.0                                 C.sub.4 H.sub.9                                                                      2.2     39.7    23.0˜24.3                                                                       C   73.5   73.4                                                               H   7.9    8.3                                 C.sub.7 H.sub.15                                                                     2.6     40.6    36.0˜36.7                                                                       C   75.2   75.0                                                               H   9.3    9.1                                 ______________________________________                                    

EXAMPLE 9 (Application example 1)

A liquid crystal composition consisting of

    ______________________________________                                        4'-fluorophenyl ester of trans-4-pentylcyclo-                                 hexanecarboxylic acid    one part,                                            4'-fluorophenyl ester of trans-4-                                             hexylcyclohexanecarboxylic acid                                                                        one part, and                                        4'-fluorophenyl ester of trans-4-                                             heptylcyclohexanecarboxylic acid                                                                       3 parts,                                             ______________________________________                                    

has a N-I point of 29.4° C. and a Δε of +1.4. The characteristicproperties of this composition were measured at 25° C. in a cell of 10μm thick provided with tin oxide transparent electrodes each coated withsilicon oxide and subjected to rubbing treatment. Its threshold voltageand saturation voltage were 1.8 V and 2.6 V, respectively.

EXAMPLE 10 (Application example 2)

A liquid crystal composition consisting of

    ______________________________________                                        4'-fluorophenyl ester of trans-4-pentylcyclo-                                 hexanecarboxylic acid    one part,                                            4'-fluorphenyl ester of trans-4-                                              hexylcyclohexanecarboxylic acid                                                                        one part, and                                        4'-fluorophenyl ester of trans-4-                                             heptylcyclohexanecarboxylic acid                                                                       4 parts                                              ______________________________________                                    

has a N-I point of 30.0° C. and a Δε of 1.51. The characteristicproperties were measured in the same manner as in Application example 1.Its threshold voltage and saturation voltage at 25° C. were 1.44 V and2.12 V, respectively, and its rise time and decay time at 3 V and 32 Hzwere 140 m sec. and 160 m sec., respectively. Further its thresholdvoltage and saturation voltage at 15° C. were 1.91 V and 2.74 V,respectively.

EXAMPLE 11 (Application example 3)

A liquid crystal mixture A consisting of

    ______________________________________                                        4-pentyl-4'-cyanobiphenyl                                                                      45%,                                                         4-heptyl-4'-cyanobiphenyl                                                                      29%,                                                                                          (Mixture A)                                  4-octyloxy-4'-cyanobiphenyl                                                                    15%, and                                                     4-pentyl-4"-cyanoterphenyl                                                                     11%,                                                         ______________________________________                                    

has a N-I point of 63.3° C., a Δε of 12.4 and a viscosity at 20° C. of60 cp. Its threshold voltage and saturation voltage at 25° C. weremeasured under the same conditions as in Application example 1 to give1.65 V and 2.31 V, respectively. A liquid crystal composition obtainedby adding 4'-fluorophenyl ester of 4-butylbenzoic acid (20 parts) of thepresent invention to the above liquid crystal mixture A (80 parts), hada lowered N-I point of 44° C. and a lowered Δε of 11.6° C., neverthelesshad lowered actuation voltages (threshold voltage: 1.31 V, saturationvoltage: 1.91 V), and also had a lowered viscosity at 20° C. of 50 cp.

EXAMPLE 12 (Application example 4)

A liquid crystal mixture obtained by adding 4'-fluorophenyl ester of4-hexyloxybenzoic acid (20 parts) to the liquid crystal mixture A (80parts) described in Application 3 had a N-I point of 48.6° C., a Δε of11.7 and a viscosity at 20° C. of 45 cp. Its threshold voltage andsaturation voltage were measured under the same conditions as inApplication 3 to give 1.45 V and 2.02 V, respectively, which were lowerthan those of the mixture A.

EXAMPLE 13 (Application example 5)

A liquid crystal composition obtained by adding 4"-fluorophenyl ester of4-(trans-4'-pentylcyclohexyl)benzoic acid (10 parts) to the liquidcrystal mixture A (90 parts) described in Application example 3 had aN-I point of 70.2° C., a Δε of 12.1 and a viscosity at 20° C. of 60 cp.Its threshold voltage and saturation voltage measured under the sameconditions as in Application example 3 were 1.77 V and 2.56 V,respectively.

EXAMPLE 14 (Application example 6)

A liquid crystal composition was prepared which consisted of

    ______________________________________                                        trans-4-propyl-(4'-cyanophenyl)-cyclohexane                                                             16%,                                                trans-4-pentyl-(4'-cyanophenyl)-cyclohexane                                                             16%,                                                4'-fluorphenyl ester of trans-4-pentyl-                                       cyclohexanecarboxylic acid (R = C.sub.5 H.sub.11 in                           formula (IV))             12%,                                                4'-fluorphenyl ester of trans-4-                                              hexylcyclohexanecarboxylic acid                                               (R = C.sub.6 H.sub.13 in formula (IV))                                                                   4%,                                                4'-fluorphenyl ester of trans-4-                                              heptylcyclohexanecarboxylic acid                                              (R = C.sub.7 H.sub.15 in formula (IV))                                                                  12%,                                                4'-fluorophenyl ester of trans-4-(trans-4'-                                   propylcyclohexyl)-cyclohexanecarboxylic acid                                  (R = C.sub.3 H.sub.7 in formula (VI))                                                                   20%, and                                            4"-fluorophenyl ester of trans-4-(trans-4'-                                   heptylcyclohexyl)-cyclohexanecarboxylic acid                                  (R = C.sub.7 H.sub.15 in formula (VI))                                                                  20%.                                                ______________________________________                                    

Its nematic temperature range was measured to give -5° to +81° C.Further it had a viscosity at 20° C. of 19.2 cp and a dielectricanisotropy of +6.4. This liquid crystal composition was sealed in a cellcomposed of two glass bases each furnished with a tin oxide transparentelectrode coated with silicon oxide and subjected to rubbing treatment,and spaced at an electrode distance of 10 μm. The composition was thensubjected to measurement of its characteristic properties at 25° C. togive a threshold voltage of 1.96 V and a saturation voltage of 2.70 V.Further, when its rise time and decay time at 25° C. were measuredemploying a square wave of 32 Hz, 5 V, they were as short as 36 m sec.and 47 m sec., respectively. Even at 0° C., they were as good as 94 msec. and 220 m sec., respectively.

EXAMPLE 15 (Application example 7)

The above-mentioned mixture A in Application example 3, i.e., a liquidcrystal mixture consisting of

    ______________________________________                                        4-pentyl-4'-cyanobiphenyl                                                                             45%,                                                  4-heptyl-4'-cyanobiphenyl                                                                             29%,                                                  4-octyloxy-4'-cyanobiphenyl                                                                           15%, and                                              4-pentyl-4"-cyanoterphenyl                                                                            11%,                                                  (NI point: 63.3° C. dielectric anisotropy: +12.4),                     ______________________________________                                    

was sealed in a cell of 10 μm thick, composed of two bases, eachfurnished with a tin oxide transparent electrode coated with siliconoxide and subjected to rubbing treatment. The characteristic propertiesof this liquid crystal cell were measured at 25° C. to give a thresholdvoltage of 1.65 V and a saturation voltage of 2.31 V. A mixture of thismixture A (80 parts) with trans-4-heptylcyclohexyl ester ofp-fluorobenzoic acid of the present invention (20 parts) had a loweredN-I point of 51.5° C. and a lowered dielectric anisotropy of +8.3.Nevertheless its threshold voltage and saturation voltage measured underthe same conditions as in the previous case were also reduced down to1.54 V and 2.15 V, respectively.

EXAMPLE 16 (Application example 8)

A mixture of the mixture A in Application example 7 (80 parts) withp'-pentyloxyphenyl ester of p-fluorobenzoic acid of the presentinvention (20 parts) had a N-I point of 54.7° C. and a dielectricanisotropy of +10.8. Nevertheless its threshold voltage and saturationvoltage measured under the same conditions as in Application example 7were reduced down to 1.52 V and 2.10 V, respectively.

EXAMPLE 17 (Application example 9)

A mixture of the mixture A in Application example 7 (80 parts) withp'-hexylphenyl ester of p-fluorobenzoic acid of the present invention(20 parts) has a N-I point of 48.0° C. and a dielectric anisotropy of+10.1. Nevertheless its threshold voltage and saturation voltagemeasured under the same conditions as in the previous case were reduceddown to 1.43 V and 2.0 V, respectively.

What is claimed is:
 1. In a liquid crystalline admixture, theimprovement wherein at least one component of said admixture is ahalogenated ester derivative expressed by the general formula ##STR14##wherein X represents a group selected from the group consisting of##STR15## R represents an alkyl group or an alkoxy group, each having 1to 15 carbon atoms; and Y represents carboxyl group the symbol and thesymbol being in a trans-configuration relative to cyclohexane orbicyclohexane ring.
 2. Halogenated ester derivatives according to claim1 wherein said --Y-- in said general formula is ##STR16##
 3. Theadmixture according to claim 2 wherein said X--Y-- in said generalformula is ##STR17##
 4. The admixture according to claim 2 wherein saidX--Y-- in said general formula is ##STR18##
 5. The admixture accordingto claim 2 wherein said X--Y-- in said general formula is ##STR19## 6.The admixture according to claim 1 wherein said X-- in said generalformula is ##STR20## said Y-- is ##STR21##
 7. The admixture according toclaim 6 wherein said X--Y-- in said general formula is ##STR22##
 8. Theadmixture according to claim 6 wherein said X--Y-- in said generalformula is ##STR23##